The secretory IgA system and the morphology of the respiratory tract mucosa are being studied using two animal models. The first is a tracheal pouch constructed in the rabbit, containing 7-8 cartilage rings with intact mucosa and submucosa. Pouch fluids were shown to contain SC and SIgA, an immunoflouresence of histological sections demonstrated a normal distribution. The second model is an in-vitro culture system of rabbit tracheal epithelial cells in monolayer. We have demonstrated normal cellular and ciliary morphology and the secretion of secretory component. These two systems will be infected with various viruses or viral components to determine their effects on morphology and functional characteristics or respiratory tract mucosa.